* generic/tcl.h: Reduced the use of CONST86 and eliminated
* generic/tcl.decls: the use of CONST86_RETURN to support source
code compatibility with Tcl 8.5 on those public routines passing
(Tcl_Filesystem *), (Tcl_Timer *), and (Tcl_Objtype *) values which
have been const-ified. What remains is the minimum configurability
needed to support code written for pre-8.6 headers via the new
-DUSE_COMPAT85_CONST compiler directive.
*** POTENTIAL INCOMPATIBILITY ***